Hose joint assemblies, in particular those assemblies used in fluid circuits for automotive and/or industrial processes, operate in exceedingly harsh environments. Factors including varying pressures and temperatures at different points of an assembly, varying diameters of different hoses in a particular circuit, as well as chemical exposure result in the need for highly rigorous hose assemblies. Therefore, it is difficult if not impossible to efficiently and economically manufacture large numbers of permanently shaped rubber hoses. Many previous attempts for manufacturing such assemblies have resulted in products that were not entirely reliable against leakage in use. After assembling engines and car bodies a connection between the different aggregates has to be accomplished. Due to the minor amount of space under the hood of an automotive, the rubber hoses used for the connection of engine, cooler and radiator, etc. have to be individually adapted to the various engine and car body types. The shape may often be very complex dependent on the available space under the vehicle hood.
Consequently, there is a strong need for hoses, in particular coolant hoses, having a complex shape and a good resistance to the rough environmental conditions in applications under the hood.
A further object of the present invention is the provision of coolant hoses that can easily be recycled and are of lower weight compared to hoses known in the prior art.
Additionally, a process for manufacturing of said hoses in an individual and economic manner, in particular in view of the production of limited quantities is desired.
As a material for the manufacturing of coolant hoses thermoplastic polymers, such as thermoplastic elastomers have been established in the last few years. Thermoplastic elastomers (TPE) combine both thermoplastic and elastic properties. Compared to the use of vulcanizable, non-thermoplastic rubbers, a separate vulcanizing step that affords a high temperature treatment of the shaped unvulcanized hoses is not necessary anymore.
In order to achieve the desired resistance against high temperatures and working pressures a reinforcement of the thermoplastic elastomers is necessary.
For several reasons the use of short fiber reinforced thermoplastic elastomers is mandatory for producing shaped articles, such as for permanently curved hoses, by the process according to the present invention:                The reinforcement must be present in the stock before it is extruded. An extrudate without any fiber reinforcement would collapse after leaving the die orifice.        The dispersed short fibers provide the hot extruded shaped article with structural integrity thus minimizing shape distortion before solidification of the extrudate.        The fiber reinforcement reduces the expansion of, for instance, a vehicle radiator hose during its use under elevated temperatures and pressures.        
However, the inherent characteristic of the polyolefinic thermoplastic elastomer blends is its non-reactive surface. To achieve adhesion between the reinforcing fibers and the embedding thermoplastic matrix the reinforcing fibers have to be modified with a polar material in order to be cohesively bondable to polar substrates.
Due to their low surface tension (28-30 dyns/cm) polyolefinic thermoplastic elastomer blends as well as polyolefinic materials, such as polyethylene or polypropylene, cannot adhere directly to more polar substrates, such as polyamid, polyester, metal and glass.
Various techniques, such as chemical surface treatment, compound modification via polar ingredients, surface oxidation or reducing surface tension of polar substrates by using a primer/adhesive system have been used to increase the surface tension of polyolefinic materials.
U.S. Pat. No. 2,911,321 describes a method for bonding a polyolefin layer on polyester using an “anchoring agent” of isocyanate/blocked isocyanate that is applied to the substrate as a dilute solution in organic solvent. The polyolefin is extruded onto the treated polyester substrate and bonded by heat and pressure.
U.S. Pat. No. 4,345,004 describes a method of forming an olefinic coating on a (metal) substrate by applying a multi-layer film of epoxy resin, olefinic resin and modified olefinic resin, then heat bonding an olefinic resin layer thereto.
U.S. Pat. No. 4,732,632 describes a method of coating a substrate by applying a liquid, curable polymer composed of resin (e.g. epoxy; polyurethane precursor) and curative (e.g. isocyanurate) to the substrate, then applying a layer of polymer (e.g. polyolefin, EPDM, butyl, etc.) that can interact chemically or physically with the curable first layer.
U.S. Pat. No. 6,300,418 discloses a thermoplastic elastomer composition comprising a thermoplastic rubber containing a fully cured rubber and a thermoplastic polyolefin, a functionalized polyolefin and additives such as crosslinker and reinforcing fibers, e.g. carbon fibers.
U.S. Pat. No. 6,072,003 discloses a composition comprising a thermoplastic elastomer, a modified polyolefin and additives like fillers.
Saikrasun et al. in “Kevlar reinforcement of polyolefin-based thermoplastic elastomer”, POLYMER, Elsevier Science Publishers B.V., GB, Vol. 40, Nr. 23 Pages 6437-6442 discloses a fiber reinforced thermoplastic elastomer comprising a thermoplastic elastomer, a modified polyolefin and a surface modified reinforcing aramid fiber.
International published patent application WO 03/062309 relates to a fiber reinforced rubber composition for tires comprising adhesively activated fibers in combination with melamine type crosslinking agents.
Nevertheless, reinforced elastomeric articles comprising the adhesion systems known in the art show an undesired sensitivity to humidity. Since humidity is inevitably present in vehicle cooling systems, it has been a further object of the present invention to provide an adhesion system that is less sensitive to humidity/moisture and that is suitable for coolant hoses to be used in cooling water circuits of automotive engines.
A further aspect of the present invention relates to the method of manufacturing shaped articles like cooling hoses.
By using a special die geometry, as disclosed, for instance by L. A. Goettler, A. J. Lambright, R. I. Leib and P. J. DiMauro at the meeting of the Rubber Division of the American Chemical Society on 7-10 Oct. 1980 in Detroit, Mich., the reinforcing short fibers (generally of less than 20 mm length) can be oriented toward the circumferential or hoop direction of the extruded hose, in order to counteract the high hoop stresses resulting from hydraulic pressure loading during use.
The economics of producing a reinforced hose structure in a single extrusion step through the use of a short fiber reinforced thermoplastic elastomer is further improved by this simplified shaping technique. Since down-line knitting and covering operations are eliminated through the use of short fiber reinforcement, the desired contour can be imposed on the hose right at the die. This is accomplished by simply moving the outer die out of the concentricity with the pin (inner die, or mandrel) or vice versa, so as to produce eccentricity in the annular die passage leading up to and including the orifice. Consequently, the resulting extrudate will bend away from the side of the die containing the wider passage.
By moving the inner or outer portions of the tube die out of the concentricity in a programmed sequence, the direction of extruding the hose can be made to deviate from the machine axis and thus to produce bends in the hose.
The mandrel die technology described above, in particular, facilitates the formation of tight bent hoses.
Nevertheless, it has been observed that burst strength is sacrificed in curving the hose despite of substantial increases in stress in the inner wall of the bend due to the wall thinning and curvature effects.
Additionally, the shapes of the articles obtained are often limited by the sterical interaction of extrudate with the extruder and/or extrusion die. This can be conceived when the hose is widely curved in a direction opposite to the extrusion direction. In this case the shaped article is extruded in the direction of the extruder.
One way to overcome the curvature effects described above is the manufacturing of hoses by blow molding. During the blow molding process the shape of a mold is transferred to the hose to be shaped. Therefore, this method necessitates molds having the individual shapes. Since the production of the molds is time and cost consumptive the production of hoses by said method, in particular in low quantities, is uneconomically.
It was therefore necessary to devise a method for the free shaping of coolant hoses that additionally avoids the curvature effects described above and which method does not necessitate expensive molds.